fix: close mcp client event loop

Author: David Padbury

src/strands/tools/mcp/mcp_client.py

@@ -330,6 +330,9 @@ async def _set_close_event() -> None:
             self._log_debug_with_thread("waiting for background thread to join")
             self._background_thread.join()
 
+            if self._background_thread_event_loop is not None:
+                self._background_thread_event_loop.close()
+
         self._log_debug_with_thread("background thread is closed, MCPClient context exited")
 
         # Reset fields to allow instance reuse